Optical wave guide driven liquid crystal display employing optical switching for input

ABSTRACT

An optical wave guide, an optical input device, fabrication methods thereof, and a liquid crystal display apparatus using the optical wave guide and optical input device are disclosed. The optical wave guide includes: a core region having a refractive index n c  through which an optical signal is transmitted; and a cladding layer in which low refractive index layers having a refractive index n 1  and high refractive index layers having a refractive index n h  are alternately deposited. A side face of the core region is covered with the cladding layer, and the refractive indices satisfy conditions of n 1  &lt;n h , and n 1  &lt;n c . The optical input device includes: a transparent substrate; the optical wave guide formed in the transparent substrate; an optical input portion; and a plurality of optical output portions for connecting a side face of the optical wave guide to a surface of the transparent substrate. The optical signal from the optical input portion is transmitted through the optical wave guide and output from the optical output portions to the outside of the transparent substrate. The liquid crystal display apparatus includes: a display medium; a plurality of pixel electrodes for driving the display medium; a plurality of signal lines; a plurality of photoconductors having photoconductive portions provided for the pixel electrodes, respectively; and the optical input device. The optical input device allowing the optical signal to selectively illuminate the photoconductive portions of the photoconductors for connecting or disconnecting the signal lines to or from the pixel electrodes.

This application is a division of application Ser. No. 08/043,477 filedApr. 7, 1993 now U.S. Pat. No. 5,455,883.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical wave guide and an opticalinput device, and fabrication methods thereof. The present inventionalso relates to a liquid crystal display apparatus which uses theoptical wave guide and the optical input device fabricated by themethods.

2. Description of the Related Art

As planer-type display apparatus, an electroluminescence panel (ELP), aplasma display panel (PDP), a liquid crystal display (LCD) and the likeare developed. Among them, the LCD can readily attain a full-colordisplay, and it can readily be connected to a large scale integratedcircuit (LSI) without using a special interface. Accordingly, the LCD isthe most promising as the planer-type display apparatus, and thetechnology related to the LCD is remarkably advanced. In recent years,methods in which optical signals are used for signal transmission hasbeen investigated for the LCD, in order to eliminate problems such assignal delay caused by an increase in size of the display apparatus, anincrease in the number of pixels to be driven, or the like.

If such optical signals are used for signal transmission, an opticalinput device is required. The optical input device is used fortransmitting light as a signal from a light source to a predeterminedportion and for inputting the light. In a conventional optical inputdevice, an optical fiber or an optical wave guide formed on a substrateis utilized.

An optical wave guide is formed on a quartz substrate, on amulticomponent glass substrate or on a plastic substrate. In the casewhere the optical wave guide is formed on the quartz substrate, a flamedeposition method is generally used. In the case where the optical waveguide is formed on the multicomponent glass substrate, an ion exchangingmethod is generally used. According to both the above methods, theoptical wave guide can be formed for either a single mode or a multimode. In the flame deposition method, a silane gas as a material gas issubjected to a combustion reaction so as to deposit it on the substrate.In the ion exchanging method, a molten salt including ions of Ag, Tl, Kor the like as a ion source are diffused in soda lime or borosilicateglass by a heating treatment. Alternatively, in the case where theoptical wave guide is formed on the multicomponent glass substrate, asputtering method can be used.

On the other hand, methods for forming an optical wave guide on asubstrate of plastic which is an organic material include a selectivephotopolymerization method, a photo-locking method or the like. In theselective photopolymerization method, polycarbonate as a base materialand methyl acrylate as a monomer are selectively exposed to ultravioletlight, so as to perform polymerization. The refractive index of themonomer is lowered by the polymerization, so that the unexposed portionbecomes an optical wave guide with a high refractive index.

In addition, an LCD in which optical signals are used for signaltransmission necessitates a transistor which performs switching bydetecting an input light beam from the optical input device.Conventionally, a pn phototransistor is employed. Regarding a materialfor photoelectric transduction in the pn phototransistor, single-crystalSi or amorphous Si (hereinafter, referred to as "a-Si") is used fordetecting light in a visible light range, and Ge, lead calcogenide, orthe like is used for detecting light in an infrared range.

Moreover, when optical signals are used in the LCD for signaltransmission, it is necessary to determine the locations of the lightsource and the optical input device. In a conventional LCD, one lightsource is provided for each of a plurality of optical input deviceswhich are disposed in parallel to each other in a row or columndirection.

In the case where an optical fiber is utilized as an optical inputdevice, there arises a problem in that the connections to other opticalcomponents are complicated. For simplifying the connections, there is anattempt to utilize an optical wave guide formed on a substrate as theoptical input device. However, this case still has a problem in that aninput/output scheme suitable for the optical wave guide has not yet beenfound.

As described above, the optical wave guide is formed on the quartzsubstrate by the flame deposition method or formed on the multicomponentglass substrate by the ion exchanging method. However, conventionally,even in a linear optical wave guide, the optical loss has a large value,i.e., 0.1 dB/cm. In a curved optical wave guide, the optical loss has afurther increased value. Therefore, the conventional optical wave guidehaving a length of 10 cm or more cannot be practically used. The reasonwhy the optical wave guide has an optical loss larger than in the caseof the optical fiber is that the interface between a side face of theoptical wave guide and the substrate may be roughed. For example, ifthere exists a rough portion having a difference in level of about 100 Åon the side face of the optical wave guide having a diameter of 1 μm,about 5% of light intensity is scattered and lost from this portion.Such a rough portion on the side face inevitably occurs by theconventional fabrication method of the optical wave guide. Therefore, incases where the optical wave guide is used, it is necessary to reducethe optical loss to a minimum by concentrating the light on a center ofwave guide so that the light intensity on the side face is decreased.

Optical loss in the optical wave guide is also caused by nonuniformityin refractive index along the propagation direction. For example, it isassumed that a fiber having a circular section with a diameter of 100 μmhas a step portion as a nonuniform portion having a diameter of 110 μmand a length of 100 μm. Even when the variation refractive index is 1%at most, 5% of total light amount is scattered from the step portion,which proves that the nonuniformity severely affects the optical loss.Therefore, in order to equally distribute light to 3000 or more pixelelectrodes in the LCD by means of the optical wave guide, a workingaccuracy in the order of 1 μm is required.

In the LCD, in order to prevent liquid crystal from being deteriorated,it is necessary to periodically reverse the polarity of voltage appliedto the liquid crystal during the drive operation. For this purpose, thecurrent direction is periodically reversed when electric charges are tobe stored in a capacitor constituted by a pixel. A conventional pnphotodiode for detecting light has a rectifying function, so thatcurrent cannot flow in the reverse direction to the pn junction.Accordingly, when a conventional pn photodiode is used for drivingpixels, the amount of current largely varies depending on the currentdirection. This results in that a time period required for storingelectric charges to a capacitor constituted by a pixel varies dependingon the current direction, whereby there arises a problem in that thecontrol is complicated.

With a construction in which a plurality of optical wave guides areconnected to a single light source, the number of light sources can bereduced and the LCD construction can be simplified. However, suchconstruction necessitates means for distributing light from the singlelight source to the plurality of optical wave guides. Unless thedistributing means can be formed in a simple structure, the LCD stillhas a complicated construction.

SUMMARY OF THE INVENTION

The optical wave guide of this invention includes: a core region havinga refractive index n_(c) through which an optical signal is transmitted;and a cladding layer in which two or more low refractive index layershaving a refractive index n₁ and two or more high refractive indexlayers having a refractive index n_(h) are alternately deposited,wherein a side face of the core region is covered with the claddinglayer, and the refractive indices satisfy conditions of n₁ <n_(h), andn₁ <n_(c).

In one embodiment, the core region is formed in a surface portion of atransparent substrate, and the cladding layer is formed to cover theside face of the core region in the transparent substrate.

In another embodiment, at least one of the low and high refractive indexlayers has a thickness between 1 nm to 10 μm in a layered direction.

In another embodiment, at least one of the thicknesses and refractiveindices of the low and high refractive index layers constituting thecladding layer are aperiodically repeated.

According to another aspect of the invention, an optical input device isprovided. The optical input device includes: a transparent substrate; anoptical wave guide formed in a surface portion of the transparentsubstrate; an optical input portion provided at one end of the opticalwave guide; and at least one or more optical output portions forconnecting a side face of the optical wave guide to a surface of thetransparent substrate, wherein light input from the optical inputportion is transmitted through the optical wave guide and output fromthe optical output portions to the outside of the transparent substrate.

In one embodiment, a refractive index of the optical output portions islarger than that of the optical wave guide.

In another embodiment, the optical output portions include means forscattering the light.

In another embodiment, the optical output portions have a refractiveindex which is increased from the center of the optical wave guide tothe surface of the transparent substrate.

According to another aspect of the invention, an optical input device isprovided. The optical input device includes: a transparent substrate; anoptical wave guide formed in a surface portion of the transparentsubstrate; an optical input portion provided at one end of the opticalwave guide; and at least one or more optical output portions forconnecting a side face of the optical wave guide to a surface of thetransparent substrate, wherein at least one of the optical input andoutput portions includes a SELFOC lens, and a sum of a mode angle oflight in the optical wave guide and an angular aperture of the SELFOClens is 90° or more, and wherein light input from the optical inputportion is transmitted through the optical wave guide and output fromthe optical output portions to the outside of the transparent substrate.

According to still another aspect of the invention, a method of formingan optical wave guide in a transparent substrate by a wet field ionexchanging method is provided. The method includes a step of diffusingions into the transparent substrate by applying a magnetic field and anelectric field in the same direction.

According to still another aspect of the invention, a liquid crystaldisplay apparatus is provided. The liquid crystal display apparatusincludes: a display medium; a plurality of pixel electrodes arranged inrow and column directions for driving the display medium; a plurality ofsignal lines arranged in the row or column direction; a plurality ofphotoconductors having photoconductive portions provided for theplurality of pixel electrodes, respectively, the photoconductorsfunctioning to connect or disconnect the signal lines to or from thepixel electrodes in accordance with an optical signal which illuminatesthe photoconductive portions; and an optical input device disposed in adirection across the plurality of signal lines, the optical input deviceallowing the optical signal to selectively illuminate thephotoconductive portions of the plurality of photoconductors. In theliquid crystal display apparatus, the optical input device includes: atransparent substrate; an optical wave guide formed in a surface portionof the transparent substrate; an optical input portion provided at oneend of the optical wave guide; and a plurality of optical outputportions for connecting a side face of the optical wave guide to asurface of the transparent substrate. In the liquid crystal displayapparatus, the optical signal input from the optical input portion istransmitted through the optical wave guide and output from the opticaloutput portions to the outside of the transparent substrate, the opticalsignal illuminating the photoconductive portions of the plurality ofphotoconductors, respectively.

In one embodiment, the optical input device further includes: a mainoptical input device constituted by part of the optical wave guide andthe optical input portion; a plurality of sub optical input devicesconstituted by another part of the optical wave guide and the pluralityof optical output portions; and a plurality of optical switch elements,provided between the main optical input device and the sub optical inputdevices, for optically connecting the main optical input device to thesub optical input devices, respectively.

In another embodiment, each of the photoconductors includes asemiconductor device having a layered structure in which three or morelayers of an n-type semiconductor layer and a p-type semiconductor layerare alternately deposited.

In still another embodiment, the layered structure further includes anintrinsic semiconductor layer between the n-type semiconductor layer andthe p-type semiconductor layer.

In still another embodiment, the pixel electrodes are directly formed onthe optical wave guide of the optical input device, and a thickness ofthe pixel electrodes is 1/10 or less of a wavelength of the lightemitted from a light source which is connected to the optical inputportion.

Thus, the invention described herein makes possible the followingadvantages:

(1) an optical signal can be input to a predetermined optical componentwith a simple structure for connection by using an optical wave guideformed on a substrate;

(2) by the provision of a light scattering portion, the output anglewith respect to a substrate can be increased, whereby light can beefficiently input;

(3) by the provision of a SELFOC lens, light can be efficiently input;

(4) by the provision of a SELFOC lens, a light source can be directlymounted on a substrate, whereby the connective structure can besimplified;

(5) by using a method according to the invention, an optical inputdevice with reduced optical loss can be fabricated;

(6) by applying the optical input device according to the inventionwhich has reduced optical loss and good transmission efficiency to aliquid crystal display apparatus, a liquid crystal display apparatuswith large capacity and high operational speed can be fabricated; and

(7) the liquid crystal display apparatus of the invention can be readilycontrolled and has a simple construction.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view showing a structure for a pixel drivingportion of a liquid crystal display apparatus in one example of theinvention.

FIG. 2 is a cross-sectional view taken along line A₁ -A₂ in FIG. 1 inone example of the invention.

FIG. 3 is an explanatory cross-sectional view of an optical scanningsignal generating portion for one example of the invention, when anoptical switch element is in an OFF state.

FIG. 4 is an explanatory cross-sectional view of the optical scanningsignal generating portion in one example of the invention, when theoptical switch element is in an ON state.

FIG. 5 is a plan view showing a display portion for one example of theinvention.

FIG. 6 is a perspective view for illustrating the connection of pixelelectrodes and signal lines for one example of the invention.

FIG. 7 is a cross-sectional view taken along line C₁ -C₂ in FIG. 6 forone example of the invention.

FIG. 8 is a partial cross-sectional view of a liquid crystal displaypanel taken along line B₁ -B₂ in FIG. 5.

FIG. 9 is a schematic cross-sectional view for illustrating thefabrication method of an optical wave guide for one example of theinvention.

FIG. 10 is a cross-sectional view showing a semi-circular lightscattering portion in one example of the invention.

FIG. 11 is a cross-sectional view showing a cylindrical light scatteringportion in one example of the invention.

FIG. 12 is a cross-sectional view perpendicular to the propagationdirection for illustrating the connection of a cylindrical lightscattering portion and an optical wave guide in one example of theinvention.

FIG. 13 is a cross-sectional view perpendicular to the propagationdirection for illustrating the connection of a semi-circular lightscattering portion and the optical wave guide for one example of theinvention.

FIG. 14 is a cross-sectional view perpendicular to the propagationdirection for illustrating the connection of a reversed semi-circularlight scattering portion and the optical wave guide for one example ofthe invention.

FIG. 15 is a cross-sectional view parallel to the propagation directionfor illustrating the connection of the cylindrical light scatteringportion and the optical wave guide in one example of the invention.

FIG. 16 is a cross-sectional view parallel to the propagation directionfor illustrating the connection of the semi-circular light scatteringportion and the optical wave guide in one example of the invention.

FIG. 17 is a cross-sectional view parallel to the propagation directionfor illustrating the connection of the reversed semi-circular lightscattering portion and the optical wave guide in one example of theinvention.

FIG. 18 is a view showing a cross-sectional structure of aphotoconductor element in one example of the invention.

FIG. 19 is a plan view showing a structure for the photoconductorelement in one example of the invention.

FIG. 20 is a cross-sectional view for illustrating the connection of anoptical wave guide and a SELFOC lens in one example of the invention.

FIG. 21 is a cross-sectional view showing an optical wave guide having alayered structure in one example of the invention.

FIG. 22 is a cross-sectional view showing an optical wave guide havingan aperiodically layered structure in one example of the invention.

FIG. 23 is a cross-sectional view showing an optical input deviceincluding high refractive index portions as optical output portionsalong the propagation direction according to the invention.

FIG. 24 is a cross-sectional view showing an optical input deviceincluding light scattering portions as optical output portions along thepropagation direction according to the invention.

FIG. 25 is a cross-sectional view showing an optical input deviceincluding a SELFOC lens as optical input and output portions along thepropagation direction according to the invention.

FIGS. 26-30 are cross-sectional views taken along line C₁ -C₂ in FIG. 6and show various structures for the photoconductive film element of theapparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, an optical wave guide, an optical input device and theirfabrication methods according to the invention will be described.

FIGS. 21 and 22 show cross sections of the optical wave guide accordingto the invention taken perpendicularly to the propagation direction. Anoptical wave guide 47 is formed in a glass substrate 11. As is shown inFIG. 21, the optical wave guide 47 is constituted of a core region 45and a cladding layer 46 which is formed so as to cover the side face ofthe core region 45. Light is transmitted through the core region 45having a refractive index n₃. In the cladding layer 46, a low refractiveindex layer 41 having a refractive index n₁ and a high refractive indexlayer 42 having a refractive index n₂ are alternately formed two or moretimes. The refractive indices of the respective layers satisfyconditions of n₁ <n_(h), n₁ <n_(c). The light transmitted from the coreregion 45 to the cladding layer 46 of the optical wave guide 47 must betransmitted from the low refractive index layer 41 to the highrefractive index layer 42. The light is totally reflected at theinterface between the low refractive index layer 41 and the highrefractive index layer 42 and transmitted back to the center of theoptical wave guide. At this time, scattered light, i.e., light which isnot reflected is transmitted to the side face of the optical wave guide47. Then, the scattered light is totally reflected at the interfacebetween the next low refractive index layer 41 and the high refractiveindex layer 42. By alternately forming the low refractive index layer 41and the high refractive index layer 42 two or more times, the intensityof light which reaches the side face of the optical wave guide 47 can bereduced. Accordingly, even if the side face of the optical wave guide 47is roughed, the light will not be lost from the side face.

If each thickness of the high refractive index layer 42 and the lowrefractive index layer 41 is several hundredth of the wavelength of thetransmitted light or less, the above effect of the invention cannot beattained. If the respective thicknesses are too large, the width and thedepth of the optical wave guide will be also too large. Therefore, atleast one of the layers preferably has a thickness in the range of 1 nmto 10 μm.

Alternatively, in the cladding layer 46, as is shown in FIG. 22, a lowrefractive index layer 43 and a high refractive index layer 44 may bealternately formed in an aperiodic manner. Specifically, thicknesses ofthe respective low refractive index layers 43 are made different fromeach other, and thicknesses of the respective high refractive indexlayers 44 are made different from each other. By forming the claddinglayer 46 so as to have the above structure on the side face of the coreregion 45, the expansion of the waveform of a electric field can besuppressed, so that the light intensity at the side face can beeffectively reduced and the optical loss can also be reduced. It isunderstood that all of the thicknesses of the low refractive indexlayers 43 are not necessarily made different, and also all of thethicknesses of the high refractive index layers 44 are not necessarilymade different. The thicknesses of the layers have only to be repeatedaperiodically. If the cladding layer 46 has a structure in which athickness of either one of the low refractive index layer 43 and thehigh refractive index layer 44 is changed in an aperiodic manner, thesame effects can be attained. Alternatively, even in a structure inwhich a refractive index of at least either one of the low refractiveindex layer 43 and the high refractive index layer 44 is changed in anaperiodic manner, the same effects can be attained.

Next, a structure for an optical input device used as a main opticalinput device 2 and a sub optical input device 4 will be described withreference to FIGS. 23, 24 and 25.

In an optical input device shown in FIG. 23, an optical wave guide 47for transmitting light into a glass substrate 11 is formed. Opticaloutput portions 6 are formed in a direction perpendicular to thepropagation direction. The optical output portions 6 are formed bycovering the optical wave guide 47 at windows 81a-81c with a materialhaving a refractive index larger than that of the optical wave guide 47.Alternatively, the optical output portions 6 may be formed by partiallyremoving the glass substrate 11 having a low refractive index whichcovers the optical wave guide 47 so as to form windows 81a-81c. Theintensity of light output from the optical output portions 6 is inproportion to an area of each of the windows 81a-81c. Accordingly, inorder to output light with the constant intensity from the respectiveoptical output portions 6, as an optical output portion becomes moreremote from the optical input portion of the optical input device, awindow of the optical output portion needs a geometrically increasedarea.

In another optical input device shown in FIG. 24, an optical wave guide47 for transmitting light into a glass substrate 11 is formed. Opticaloutput portions 6 are formed in a direction perpendicular to the lighttransmission direction. The optical output portions 6 are formed byproviding scattering portions 91a-91c in the optical wave guide 47 whichare made of a material having a refractive index smaller than that ofthe optical wave guide 47 and larger than that of the glass substrate11. The light which reaches the scattering portions 91a-91c from theoptical wave guide 47 is scattered from the scattering portions 91a-91cto the outside. Therefore, the intensity of the light output from theoptical output portions 6 is in proportion to a volume of each of thescattering portions 91a-91c. If a refractive index is made larger fromthe center toward the surface of the optical wave guide 47, the lighttransmitted into the scattering portions 91a-91c is gradually curved inthe scattering portions 91a-91c. As a result, the light is output fromthe optical output portions 6 in a direction perpendicular to thepropagation direction through the optical wave guide 47. If therefractive index is constant within the optical wave guide 47, the lightis scattered at an angle of about 10° which is substantially equal to amode angle of the optical wave guide 47.

In another optical input device shown in FIG. 25, an optical wave guide47 for transmitting light into a glass substrate 11 is formed. As anoptical input portion 110 and an optical output portion 6, a distributedindex lens (a SELFOC lens) 141 is provided. The sum of the mode angle oflight transmitted through the optical wave guide 47 and an angularaperture of the SELFOC lens 141 is set to be 90° or more. By providingsuch optical input portion 110 or optical output portion 6, light can beinput and output in a direction perpendicular to the propagationdirection through the optical wave guide 47. The intensity of the lightoutput from the optical output portion 6 is in proportion to thediameter of the SELFOC lens 141.

Next, fabrication methods of the optical wave guide and the opticalinput device according to the present invention will be described.

FIG. 9 schematically shows a cross section for explaining thefabrication method of an optical wave guide 47. Into a glass substrate11, ion species 81 for increasing the refractive index are diffused by awet field ion exchanging method. The glass substrate 11 is formed ofsoda lime or borosilicate glass containing alkali oxide. An ionexchanging vessel is kept at a temperature of 200°-700° C. A surface ofthe glass substrate 11 is smoothed to such a degree that the differencein level of the surface is to be 0.1 μm or less. Then, a mask 50 made ofa metal such as Ti or an oxide thereof is formed thereon.

The surface of the glass substrate 11 should be smooth and flat in orderthat the uniformity of an electric field across the surface may beenhanced, that the surfaces of the optical wave guide 47 to be formedmay be smooth, and that the unnecessary scattering of light may possiblybe eliminated for suppressing the attenuation of light. For the abovereasons, the value of 0.1 μm is sufficient for visible light. Forinfrared light, it is unnecessary to smooth the surface of the glasssubstrate 11 to such a degree. Then, a platinum electrode is put into asolution in the ion exchanging vessel, so that an electric-field isapplied. As a result, the ion species 81 of Ag⁺, Tl⁺, K⁺ or the like areselectively diffused into the glass substrate 11 from the side of ananode 80.

In the method according to the invention, an external magnetic field isused when the ion species 81 are diffused into the glass substrate 11.

If, in the ion exchanging vessel, the external magnetic field is appliedin a direction perpendicular to the glass substrate 11 which is parallelto the electric field, the diffusion of the ion species 81 into thesurface of the glass substrate 11 is enhanced, so as to form the opticalwave guide 47 uniformly. Moreover, since ions are held in the directionof magnetic field, the orientation thereof is ensured.

As is shown in FIG. 21, the optical wave guide 47 may be constituted bya core region 45 and a cladding layer 46 having a layered structure inwhich a low refractive index layer 41 and a high refractive index layer42 are alternately formed. More specifically, the glass substrate 11 ismade of soda lime or borosilicate glass having alkali oxide, asdescribed above. Ion species for increasing the refractive index and ionspecies for decreasing a refractive index are alternately diffused intothe glass substrate 11 by the wet field ion exchanging method. The ionexchanging vessel is kept at 200°-700° C. In this case, as masks made ofa metal such as Ti or an oxide thereof, masks each provided with alinear hole having a common length of 1 mm and a width of 100 μm, 90 μm,80 μm, 70 μm, or the like are successively formed on the smoothedsurface of the glass substrate 11. In other words, the widths of theholes are sequentially reduced by 10 μm. For each mask, a platinumelectrode is put into the solution and an electric field is applied.Thus, ion species are diffused into the glass substrate 11 from the sideof an anode. As the ion species, ion species for increasing therefractive index such as Ag⁺, Tl⁺, and K⁺, and ion species the same asthose in the glass substrate 11 are alternately diffused. As a result,as is shown in FIG. 21, in the optical wave guide 47 having asemi-circular shape in section, the cladding layer 46 can be formed tohave a layered structure in which the low refractive index layer 41 of10 μm and the high refractive index layer 42 of 10 μm are alternatelyformed. At a final step, the core region 45 is formed. In this case, forfabricating the optical wave guide 47 including the cladding layer 46having the layered structure, the ion exchanging method is used, butalternatively, another method can be used.

If the optical wave guide 47 includes the cladding layer 46 having theabove layered structure shown in FIG. 21, light transmitted through theoptical wave guide 47 should pass through some interfaces between thelow refractive index layer 41 and the high refractive index layer 42.Therefore, the light is concentrated in the vicinity of the center ofthe optical wave guide 47 and the light intensity at the side face isreduced. Therefore, even when the side face of the optical wave guide 47is rough, the optical loss due to scattering can be reduced.

In another case, as is shown in FIG. 22, the optical wave guide 47 mayinclude a cladding layer 46 having a layered structure in which a lowrefractive index layer 43 and a high refractive index layer 44 arealternately formed in an aperiodic manner. In this case, for example,masks each provided with a linear hole having a common length of 1 mmand a width of 100 μm, 95 μm, 85 μm, 75 μm, 65 μm, or the like are used.That is, the widths are reduced in the aperiodic manner. Thus, in theoptical wave guide 47 having a semi-circular shape in section, the lowrefractive index layer 43 and the high refractive index layer 44 can bealternately formed, while some layers have different thicknesses, i.e.,the thicknesses of the layers are aperiodic. Alternatively, thethicknesses of the layers may be constant, but refractive indices of thelayers may be varied in the aperiodic manner. Alternatively, both thethicknesses and the refractive indices may be changed in the aperiodicmanner. In order to change a refractive index, a dose of ion species tobe diffused in a layer is made different from that in another layer.

As described above, by aperiodically changing at least one of thethickness and the refractive index in the layered structure of thecladding layer 46, the propagation of the waveform of the electric fieldcan be suppressed. As a result, the light intensity at the side face caneffectively reduced and hence the optical loss can be reduced.

In the case where a sub optical input device in which a light scatteringportion is simultaneously formed with the optical output portion 6, theion species 81 for increasing a refractive index and ion species fordecreasing a refractive index are both diffused in the glass substrate11. In other words, in addition to the above-mentioned masks, a mask isformed so as to leave portions for the output of light to photoconductorelements at the same pitches as those of the pixel electrodes.Thereafter, ion species the same as those in the original glasssubstrate 11 are diffused. As a result, an optical wave guide having acircular shape in section and a light scattering portion are formed.

The case where the light scattering portion is used as the opticaloutput portion 6 is described in more detail. A light scattering portion91 which is formed in the above manner takes a semi-circular shape as isshown in FIG. 10 or a cylindrical shape as is shown in FIG. 11. Whenlight is output from about 3000 light scattering portions 91 at the sametime using a single light source, the size of each light scatteringportion 91 is determined as follows. The height thereof in a directionperpendicular to the propagation direction is 1/10 or less of a diameterof a core portion of the optical wave guide, and the length thereofalong the propagation direction is 1/5 or less of an interval betweenpixels.

By adjusting the size of each of the light scattering portions 91 asdescribed above, about 0.1% or lower of the optical energy in theoptical wave guide 47 can be diffused to the outside of the optical waveguide 47. In the case of a light scattering portion 91 having such asmall size, the energy of light scattered at the light scatteringportion 91 is substantially in proportion to the volume of the lightscattering portion 91. A light scattering portion 91 which is moreremote from the light source needs a geometrically increased volume.

Various connections of the light scattering portion 91 and the opticalwave guide 47 are shown in FIGS. 12-14 and FIGS. 15-17. FIGS. 12-14 showcross sections perpendicular to the propagation direction. FIGS. 15-17show cross sections along the propagation direction. The lightscattering portions 91 shown in FIGS. 12 and 15, in FIGS. 13 and 16, andin FIGS. 14 and 17 take a cylindrical shape, a semi-circular shape, anda reversed semi-circular shape, respectively. A refractive index of thelight scattering portion 91 is set between the refractive index of theglass substrate 11 and the refractive index of the optical wave guide47. The refractive indices of the light scattering portions 91 may beconstant or changed depending on the positions thereof. In the case ofconstant refractive indices, the angle of light scattering is relativelysmall, e.g., 10° which is substantially equal to the mode angle of theoptical wave guide 47. In the case where the refractive indices aredistributed as in the distributed index lens (SELFOC lens), the lightcan be perpendicularly output from the optical wave guide 47.

The shape of the optical wave guide 47 may be circle or square insection. In the case of a planer-type optical wave guide, theabove-mentioned core diameter of the optical wave guide 47 correspondsto the width of the optical wave guide 47. In an alternative case, theoptical wave guide 47 and the light scattering portion 91 may not besimultaneously formed. Specifically, the light scattering portion 91 maybe formed after the formation of the optical wave guide 47.

Next, the connection of the light source 1 and the main optical inputdevice 2 having the optical input portion 110 is described. In thisexample, a light emitting diode (LED) for visible light is used as thelight source 1. FIG. 20 is a cross-sectional view for explaining theconnection of the optical wave guide 47 and the SELFOC lens 141. Thelight source 1 is disposed above the SELFOC lens 141. Unless the sum ofthe angular aperture β of the SELFOC lens 141 and the mode angle α oflight is 90° or more, the light cannot be effectively input to andoutput from an optical wave guide. If the SELFOC lens 141 is formed on aglass substrate, the angular aperture thereof can be 35°-70°. In thiscase, the SELFOC lens 141 is connected to the main optical input device2 having the mode angle of 0°-55°, and the angular aperture of theSELFOC lens 141 is set to be 60°. The optical loss in the connection tothe light source 1 was 3 dB.

Hereinafter, an example of a liquid crystal display apparatus using theabove optical wave guide and the optical input device according to theinvention will be described with reference to the relevant figures.

FIG. 1 is a schematic view showing a structure of a pixel drivingportion of the liquid crystal display apparatus in this example. Theliquid crystal display apparatus includes an optical scanning signalgenerating portion 19 and a display portion 20.

In the optical scanning signal generating portion 19, a main opticalinput device 2 is disposed. A light source 1 is connected to an opticalinput portion 110 of the main optical input device 2. A plurality of suboptical input devices 4 are connected to the main optical input device 2via respective optical switch elements 3.

In the display portion 20, the sub optical input devices 4 are arrangedin parallel to each other along a row direction. A plurality of datasignal lines 8 are arranged along a column direction. In the vicinitiesof the crossings of the data signal lines 8 and the sub optical inputdevices 4, photoconductor elements 5 having photoconductive films 7 aredisposed. The photoconductive films 7 are disposed in such a manner thatthey are in contact with a plurality of optical output portions 6provided in the sub optical input devices 4, respectively. Each of thephotoconductor elements 5 is connected to a pixel electrode 9. The pixelelectrode 9, liquid crystal and a counter electrode constitute a pixel10.

The light emitted from the light source 1 is transmitted to the mainoptical input device 2. Then, the light passes through a selected one ofthe plurality of optical switch elements 3. Almost all of the lightwhich has passed through the selected optical switch element 3 is guidedinto the corresponding one of the sub optical input devices 4. Part ofthe guided light is output from the optical output portion 6 of the suboptical input device 4 and illuminates the photoconductive film 7, so asto make the photoconductor element 5 conductive. The photoconductorelement 5 in the conductive state drives the pixel 10.

FIG. 2 is a cross-sectional view taken along line A₁ -A₂ in FIG. 1.FIGS. 3 and 4 show cross sections along the main optical input device 2for explaining the optical scanning signal generating portion 19. Thestructure and operation of the optical switch element 3 in the liquidcrystal display apparatus in this example will be described, referringto FIGS. 2-4.

As is shown in FIGS. 2-4, in the optical scanning signal generatingportion 19, the sub optical input device 4 is formed on a surface of aglass substrate 11. The main optical input device 2 is formed on asurface of a glass substrate 13. The glass substrates 11 and 13 aredisposed so that the surface on which the main optical input device 2faces the surface on which the sub optical input devices 4 are formed,via a spacer 18. A space formed by the spacer 18, and the glasssubstrates 11 and 13 is filled with liquid crystal 17. The opticalswitch element 3 includes liquid crystal 17, part of the main opticalinput device 2 and part of the sub optical input device 4.

As is shown in FIGS. 3 and 4, on the surface of the glass substrate 13on which the main optical input device 2 has been formed, a plurality oftransparent segment electrodes 21 are formed. On the surface of theglass substrate 11 on which the sub optical input devices 4 have beenformed, a plurality of transparent common electrodes 22 and a pluralityof common metal electrodes 23 for electrically connecting the pluralityof transparent common electrodes 22 to each other are formed.

Such a structure can be realized by using liquid crystal as a claddingmaterial in the optical switch. This structure has an advantage in thatit can readily be produced in a small size.

Next, a fabrication method for an optical switch element is described.

In stead of the glass substrates 11 and 13, it is possible to useplastic substrates. A refractive index of glass is selected from valuesin the range of about 1.45 to 1.95 depending on the composition thereof.Refractive indices of the main optical input device 2 and the suboptical input device 4 are made larger than the refractive indices ofthe glass substrates 11 and 13 by 0.5-5%. A refractive index of theliquid crystal 17 used in the optical switch element 3 varies dependingon the composition thereof and the orientation direction of liquidcrystal molecules with respect to the optical axis. The refractive indexof the liquid crystal 17 also varies depending on voltages appliedthereto. The liquid crystal 17 has two refractive indices n₁ and n₂depending on voltages applied thereto. The refractive index of theliquid crystal 17 is selected so as to satisfy a condition of 1.45<n₁<n₂ <1.8. A difference between n₁ and n₂ is set to be about 0.1-0.2.Materials for the main and sub optical input devices 2 and 4 and theliquid crystal 17 are selected so that the refractive indices thereofsatisfy these requirements.

In this example, KB7 glass is selected for the glass substrate 13 (therefractive index n_(A0) =1.52). Ions of Ag are diffused in optical waveguide portions by the wet field ion exchanging method. Thus, the mainoptical input device 2 having a stripe shape and a refractive indexn_(A1) =1.55 is formed to have a width of 50 μm, and a depth of 50 μm.For the glass substrate 11, KzF1 glass (the refractive index n_(B0)=1.55) is selected. Ions of Tl are diffused in desired portions. Thus,the sub optical input device 4 having a stripe shape and a refractiveindex n_(B1) =1.63 is formed to have a width of 50-70 μm, and a depth of30 μm. The transparent segment electrodes 21 and the transparent commonelectrodes 22 are formed in such a manner that In₂ O₃ is deposited tohave a thickness of 50 nm and patterned by photolithography and etchingtechniques. For the orientation process toward a wall with which theliquid crystal molecules are in contact, SiO₂ is obliquely deposited.For the liquid crystal 17, ferroelectric liquid crystal (3M2CPOOB:(2S,3S)-3-methyl-2-chloropentanoic acid-4',4"-octyloxybiphenylester; n₁'=1.49, n₂ '=1.60) or the like is used.

Next, the operation of the optical switch element 3 is described withreference to FIGS. 3 and 4.

Liquid crystal molecules of the liquid crystal 17 are rotated by ±30°with respect to the orientation axis depending on the applied electricfield direction (a positive field or a negative field). In the opticalswitch element 3 made of the above material, when voltage of a positivefield is applied so that the liquid crystal molecules are at rightangles with the incident light, the refractive index n₂ of the liquidcrystal 17 is equal to n₂ =1.60. When voltage of a negative field isapplied, the liquid crystal molecules are rotated by 60° in a negativedirection. At this time, the refractive index n₁ of the liquid crystal17 is 1.52 which is obtained by the following equation:

    n.sub.1 =[n.sub.1'.sup.2 ·n.sub.2 '.sup.2 /(n.sub.2 '.sup.2 ·sin.sup.2 θ+n.sub.1 '.sup.2 ·cos.sup.2 θ)].sup. 1/2

where θ is an angle formed by the optical axis and the liquid crystalmolecules.

When a negative voltage is applied to the liquid crystal 17, the opticalswitch element 3 is in an OFF state. At this time, the liquid crystal 17has the refractive index n₁ of 1.52. Refractive indices n_(A0) andn_(A1) of the glass substrate 13 and the main optical input device 2satisfy conditions of n_(A0) <n_(A1) and n_(A1) >n₁. Therefore, as isshown in FIG. 3, the light is confined in the main optical input device2 and repeatedly and totally reflected, so as to be transmitted withinthe main optical input device 2.

When a positive voltage is applied to the liquid crystal 17, the opticalswitch element 3 is in an ON state. At this time, the liquid crystal 17has a refractive index n₂ of 1.60, and refractive indices of therespective portions satisfy conditions of n_(A0) <n_(A1), n_(A1) <n₂<n_(B1), and n_(B1) >n_(B0) (where, n_(B0) and n_(B1) denote refractiveindices of the glass substrate 11 and the sub optical input device 4).Therefore, as is shown in FIG. 4, the light transmitted within the mainoptical input device 2 passes through the liquid crystal 17 rather thanbeing totally reflected. Then, the light is guided into and confined inthe sub optical input device 4 which is opposite to the main opticalinput device 2.

In the above-mentioned manner, one of the plurality of optical switchelements 3 is sequentially switched to the ON state from the top one tothe bottom one in the figures, and the other optical switch elements 3are switched to the OFF state. As a result, almost all of light emittedfrom the light source 1 is sequentially guided to the aimed sub opticalinput devices 4, and hence the optical scanning can be efficientlyperformed.

Next, the structure of the display portion 20 will be described below.

The display portion 20 is connected to the optical scanning signalgenerating portion 19 via the glass substrate 11 and the sub opticalinput device 4 which is formed on the surface of the glass substrate 11.In the display portion 20, a space formed by the glass substrates 11 and15 and spacers 18 is filled with liquid crystal 16 which constitutespixels.

FIG. 5 is a plan view showing the display portion 20. FIG. 6 is aperspective view for explaining the connections of pixel electrodes andsignal lines. FIG. 7 shows a cross section taken along line C₁ -C₂ inFIG. 6. FIG. 8 shows a cross section taken along line B₁ -B₂ in FIG. 5.

The display portion 20 includes pixels arranged in m rows and n columns.The liquid crystal is of a twisted nematic (TN) type. As is shown inFIG. 5, on a substrate, pixel electrodes 9 (P₁,1 -_(P) _(m),n) arearranged in a matrix, i.e., m pixel electrodes along a row direction andn pixel electrodes along a column direction are disposed.

For the pixel electrodes 9 (P₁,1 -P_(m),n), photoconductor elements 5(S₁,1 -S_(m),n) are provided, respectively. For columns of the pixelelectrodes 9, i.e., P₁,1 -P₁,n, P₂,1 -P₂,n, . . . and P_(m),1 -P_(m),n,data signal lines 8 (X₁ -X_(m)) extending in the column direction areformed, respectively, on the same substrate. The data signal lines 8 (X₁-X_(m)) are respectively connected to the columns of pixel electrodes 9(P₁,1 -P₁,n, P₂,1 -P₂,n, . . . and P_(m),1 -P_(m),n), via thephotoconductor elements 5 (S₁,1 -S₁,n, S₂,1 -S₂,n, . . . and S_(m),1-S_(m),n), respectively.

Corresponding to the rows of pixel electrodes 9, i.e., the rows ofphotoconductor elements 5 (S₁,1 -S_(m),1, S₁,2 -S_(m),2, . . . and S₁,n-P_(m),n), sub optical input devices 4 (Y₁ -Y_(n)) extending in the rowdirection are formed in the same substrate.

In order to selectively apply light to the photoconductor elements 5(S₁,1 -S_(m),n), the sub optical input devices 4 (Y₁ -Y_(n)) areprovided under the photoconductor elements 5 (S₁,1 -S_(m),n) and thepixel electrodes 9 (P₁,1 -P_(m),n). As is shown in FIGS. 6 and 7, on aglass substrate 11, a sub optical input device 4 extending in the rowdirection is provided. On the surface of the glass substrate 11 on whichthe sub optical input devices 4 have been formed, photoconductive films7 of the photoconductor elements 5 are formed. The photoconductive film7 is formed so as to electrically connect or not to connect the pixelelectrode 9 with the data signal line 8 which extends in the columndirection.

Referring to FIG. 8, the display portion 20 will be described in detail.

A counter electrode 55 is formed on a surface of a glass substrate 15. Apolyimide film 58 is formed on the entire surface of the glass substrate15 including the counter electrode 55. The glass substrates 11 and 15are disposed in parallel so that the pixel electrode 9 faces the counterelectrode 55 with a spacer 18 interposed therebetween. A space formed bythe glass substrates 11 and 15, and the spacer 18 is filled with liquidcrystal 16. On the surface of the glass substrate 11 on which the pixelelectrodes 9 have been formed, a base film 57 for an orientation film isformed.

Next, the operation of the display portion 20 will be described.

A scanning signal coupled to an optical switch element 3 is transmittedat a predetermined timing, and light is guided to the corresponding oneof the sub optical input devices 4 (Y₁ -Y_(n)). The light illuminatesthe corresponding photoconductor elements 5 (S₁,1 -S_(m),n). Thephotoconductor elements 5 usually have high impedance. When illuminated,the photoconductor elements 5 are changed to have low impedance, so asto selectively and electrically connect the data signal lines 8 (X₁-X_(m)) to the corresponding pixel electrodes 9 (P₁,1 -P_(m),n). Byapplying this voltage to pixel electrodes, pixels can be driven.

Hereinafter, a structure and a fabrication method for a photoconductorelement is described in more detail. A photoconductor element may have astructure shown in FIG. 18 instead of the structure shown in FIG. 7. Inthe structure shown in FIG. 18, the photoconductor element is disposedon a light scattering portion 91. A column direction signal line 128 isformed on a photoconductive film 7 with an insulator 122 interposedtherebetween. The photoconductive film 7 serves as a switch foroptically controlling an electric signal between the column directionsignal line 128 and a pixel electrode 129.

In the case where the wavelength of incident light is 1 μm or less, amaterial for the photoconductive film may be polycrystalline Si, ora-Si. Preferably, an element structure should be a photodiode of ajunction type selected from npn (reference 7a, FIG. 26), pnp (reference7b, FIG. 27), npnp (reference 7c, FIG. 28), pnpn (reference 7d, FIG.29), and nipin (reference 7e, FIG. 30). In another case where incidentlight is near infrared radiation, a material for the photoconductivefilm may be polycrystalline PbS, PbSe Te, or mixed crystals thereof. Inthis case, for regulating the amount of current flowing through theelement, p-type or n-type impurities are added.

In this case, as is shown in FIG. 19, electrodes 132 of gold or the likeare provided at both ends of a photoconductive film 131, so as toconnect a column direction signal line to a pixel electrode. For thepurpose of efficient photoelectric transduction, the length of thephotoconductive film 131, i.e., the distance between the electrodes 132is increased, in order that the photoconductive area is increased, andthat a resistance in the case of no light illumination is increased.Alternatively, a-Si or a-SiN may be used for the photoconductive film.

Next, referring to FIG. 8, a fabrication method of the display portion20 is mainly described. First, In₂ O₃ is deposited to have a thicknessof 500 Å on the entire surface of a glass substrate 11. Then, pixelelectrodes 9 and common electrodes 22 of optical switch elements 3 (FIG.3) are simultaneously formed by photolithography and etching techniques.Each of the pixel electrodes 9 partially overlaps the above-mentionedsub optical input device 4. On the overlap portion, a photoconductorelement 5 is formed.

The pixel electrode 9 (In₂ O₃) also functions as one of the electrodesof the photoconductor element 5. Then, a-Si is deposited to have athickness of about 1-2 μm by a plasma CVD method, and patterned by thephotolithography and etching techniques to form a photoconductive film7. Thereon, a metal such as Ni, Al, or the like is deposited to have athickness of about 2000-5000 Å. The deposited metal is patterned byetching to simultaneously form data signal lines 8 and common metalelectrodes 23 for connecting the common electrodes to each other (FIG.3).

Thereafter, SiO₂ is deposited onto the entire surface. The SiO₂ filmserves as a base film 57 for an orientation film which will be depositedin the next step. That is, due to the SiO₂ film, the liquid crystalmolecules are better orientated. Some liquid crystal materials do notnecessitate such a base film. Next, for the orientation process toward awall with which the liquid crystal molecules are in contact, SiO₂ isobliquely deposited. These SiO₂ films may also have an orientationprocess effect on the side of the glass substrate 11 which is in contactwith the ferroelectric liquid crystal 17 in the optical scanning signalgenerating portion 19.

In this structure, the sub optical input device 4 is in contact with thephotoconductive film 7 (a-Si), the base film for orientation 57 (SiO₂),the orientation film (SiO₂), and the liquid crystal 16, via the pixelelectrodes 9. Refractive indices of the respective materials are shownas follows: 2.0 for In₂ O₃, 3.5 for a-Si, 1.46 for SiO₂, 1.52-1.60 forliquid crystal, and 1.63 for the sub optical input device 4.

However, the thickness of the In₂ O₃ film functioning as the pixelelectrode 9 is as small as 500 Å which is one-tenth when compared withthe wavelength of light. Therefore, the In₂ O₃ film is negligible forconsidering a cladding material in the optical wave guide. Accordingly,although part of light in the sub optical input device 4 illuminates thea-Si film, the remaining light will not be scattered because thematerials with which the sub optical input device 4 is in contact haverefractive indices lower than that of the sub optical input device 4. Asdescribed above, if the thickness of the In₂ O₃ film is set to be 1/10or less as compared with the wavelength of light, the effect of the In₂O₃ film is negligible.

On the other hand, on a glass substrate 15, In₂ O₃ is deposited to havea thickness of 1500 Å, and etched to form a counter electrode 55. To thesurface of the glass substrate 15, a polyimide film 58 with a thicknessof about 500 Å is applied and rubbed, which is used as a horizontalorientation agent for liquid crystal.

The glass substrates 11 and 15 are laminated to each other with asealing member in such a manner that they are spaced by a predetermineddistance using spacers 18 of 5 μm which are interposed therebetween.Into the space between the substrates, liquid crystal 16 of PCH(phenylcyclohexan) type as a display medium is injected under vacuum andsealed. Thus, a liquid crystal panel is completed.

Hereinafter, the operation of the liquid crystal display apparatus inthis example is described.

By applying voltage between the transparent segment electrode 21 and thetransparent common electrode 22 shown in FIG. 3, the light which isemitted from the light source 1 and transmitted through the main opticalinput device 2 is guided into one of the sub optical input devices 4(e.g., Y₁) via the selected optical switch element 3. Then, the lightilluminates the photoconductor elements 5 (S₁,1 -S_(m),1) formed on thesub optical input device 4 (Y₁). When illuminated, the photoconductorelements 5 (S₁,1 -S_(m),1) are decreased in impedance so as to beconductive. As a result, the data signal lines 8 (X₁ -X_(m)) and thecorresponding pixel electrodes 9 (P₁,1 -P_(m),1) are electricallyconnected, respectively.

Therefore, data signals which represent a display pattern currentlyinput onto the data signal lines 8 (X₁ -X_(m)) are simultaneouslysupplied to the pixel electrodes 9 (P₁,1 -P_(m),1) along the selectedrow.

In the above-mentioned manner, the light from the light source 1 issequentially guided into the respective sub optical input devices 4.Thus, the data signal lines 8 (X₁ -X_(m)) are electrically connected tothe respective rows of pixel electrodes 9 (P₁,1 -P_(m),1, P₁,2 -P_(m),2,. . . , P₁,n -P_(m),n) in a sequential manner. Due to the electricconnection, data signals which represent a display pattern currentlyinput onto the data signal lines 8 (X₁ -X_(m)) are simultaneouslysupplied to the pixel electrodes 9 in each row.

When a selection period which is started by the illumination of thephotoconductor elements 5 is over, a non-selection period (during thisperiod, the photoconductor elements 5 are not illuminated) started. Inthe non-selection period, the photoconductor elements 5 a re in the highimpedance state. Therefore, charges which have been charged in the pixelelectrode 9 are held in a capacitor 10 of a liquid crystal element untilthe next selection period is started.

This driving system is the same as a conventional driving system for anactive matrix driving type LCD which uses 3-terminal non-linear typeelements. The conventional TFT-LCD has a disadvantage in that a gatesignal is leaked to a pixel electrode 9 due to a parasitic capacitancebetween a gate electrode and a drain electrode coupled to the pixelelectrode 9. On the contrary, in the LCD apparatus according to thepresent invention, one of two sets of signal line groups on the side ofa scanning electrode is formed as an optical wave guide, so that the LCDapparatus of the invention eliminates the disadvantage in the prior art.Therefore, there exist no problems such as reduction in contrast,persistence, shortage in lifetime, which are associated with thedistortion on the pixel electrode 9 of a voltage waveform which issymmetrical for positive and negative polarities of a signal caused by adirect current component.

Moreover, in the conventional TFT-LCD, a gate signal is attenuated dueto parasitic capacitances for one scanning on one gate electrode and awiring resistance, whereby the contrast is reduced and the display isdeteriorated to be non-uniform. On the contrary, the display apparatusof this example adopts an optical scanning system, whereby problems dueto parasitic capacitances and any wiring resistance are not found.

In the above-described example, the optical scanning signal generatingportion 19 is provided at one side of the sub optical input device 4,and the single light source 1 is provided at one and upper side.Alternatively, the optical scanning signal generating portions 19 may beprovided at both sides of the sub optical input device 4. In anotherexample, the optical scanning signal generating portion 19 at one sideis divided into upper and lower portions, and light sources 1 areprovided for the upper and lower portions, respectively. In this case,the number of employed light sources 1 is four.

Furthermore, if a color filter is attached to the glass substrate 15, orif the liquid crystal is of a color display mode such as a guest-hostmode, a reflection-type or a transmission-type full-color or multicolordisplay can be attained.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed is:
 1. A liquid crystal display apparatus comprising:adisplay medium; a plurality of pixel electrodes arranged in row andcolumn directions for driving said display medium: a plurality of signallines arranged in the row or column direction; a plurality ofphotoconductors having photoconductive portions provided for saidplurality of pixel electrodes, respectively, said photoconductorsfunctioning to connect or disconnect said signal lines to or from saidpixel electrodes in accordance with an optical signal which illuminatessaid photoconductive portions; and an optical input device, a part ofsaid optical input device being disposed in a direction across saidplurality of signal lines, said optical input device allowing saidoptical signal to selectively illuminate said photoconductive portionsof said plurality of photoconductors, wherein said optical input deviceincludes: a transparent substrate; a plurality of optical wave guidesformed in a surface portion of said transparent substrate; an opticalinput portion provided at one end of said optical wave guide; aplurality of optical switch elements provided with said plurality ofoptical wave guides, respectively: and a plurality of optical outputportions for connecting a side face of said optical wave guide to asuffice of said transparent substrate; and wherein said plurality ofswitch elements optically connecting one of said plurality of opticalwave guides selectively, said optical signal input from said opticalinput portion is transmitted through said one of optical wave guide andoutput from said optical output portions to the outside of saidtransparent substrate, said optical signal illuminating saidphotoconductive portions of said plurality of photoconductors,respectively.
 2. An apparatus according to claim 1, wherein each of saidphotoconductors includes a semiconductor device having a layeredstructure in which three or more layers of an n-type semiconductor layerand a p-type semiconductor layer are alternately deposited.
 3. Anapparatus according to claim 2, wherein said layered structure furtherincludes an intrinsic semiconductor layer between said n-typesemiconductor layer and said p-type semiconductor layer.
 4. An apparatusaccording to claim 1, wherein said optical input device includes asingle light source.
 5. An apparatus according to claim 4, wherein saidlight source has a single opening for emitting a light into said opticalinput portion.
 6. A liquid crystal display apparatus comprising:adisplay medium; a plurality of pixel electrodes arranged in row andcolumn directions for driving said display medium; a plurality of signallines arranged in the row or column directions; a plurality ofphotoconductors having photoconductive portions provided for saidplurality of pixel electrodes, respectively, said photoconductorsfunctioning to connect or disconnect said signal lines to or from saidpixel electrodes in accordance with an optical signal which illuminatessaid photoconductive portions; and an optical input device disposed in adirection across said plurality of signal lines, said optical inputdevice allowing said optical signal to selectively illuminate saidphotoconductive portions of said plurality of photoconductors, whereinsaid optical input device includes: a transparent substrate; a mainoptical input device comprising a part of an optical wave guide formedin a surface portion of said transparent substrate and an optical inputportion provided at one end of said optical wave guide; a plurality ofoptical output portions for connecting a side face of said optical waveguide to a surface of said transparent substrate, and a plurality of suboptical input devices constituted by another part of said optical waveguide and said plurality of optical output portions: and a plurality ofoptical switch elements with liquid crystal cladding layer, providedbetween said main optical input device and said sub optical inputdevices, for optically connecting said main optical input device to saidsub optical input devices, respectively; wherein said optical signalinput from said optical input portion is transmitted through saidoptical wave guide and output from said optical output portions to theoutside of said transparent substrate, said optical signal illuminatingsaid photoconductive portions of said plurality of photoconductors,respectively.
 7. A liquid crystal display apparatus comprising:a displaymedium: a plurality of pixel electrodes arranged in row and columndirections for driving said display medium; a plurality of signal linesarranged in the row or column directions; a plurality of photoconductorshaving photoconductive portions provided for said plurality of pixelelectrodes, respectively, said photoconductors functioning to connect ordisconnect said signal lines to or from said pixel electrodes inaccordance with an optical signal which illuminates said photoconductiveportions: and an optical input device disposed in a direction acrosssaid plurality of signal lines, said optical input device allowing saidoptical signal to selectively illuminate said photoconductive portionsof said plurality of photoconductor, wherein said optical input deviceincludes: a transparent substrate; an optical wave guide formed in asurface portion of said transparent substrate; an optical input portionprovided at one end of said optical wave guide; and a plurality ofoptical output portions for connecting a side face of said optical waveguide to a surface of said transparent substrate: and wherein said pixelelectrodes are directly formed on said optical wave guide of saidoptical input device, and a thickness of said pixel electrodes is 1/10or less of a wavelength of the light emitted from a light source whichis connected to said optical input portion, and said optical signalinput from said optical input portion is transmitted through saidoptical wave guide and output from said optical output portions to theoutside of said transparent substrate, said optical signal illuminatingsaid photoconductive portions of said plurality of photoconductors,respectively.